ADPKD is a systemic disorder characterized by cysts involving multiple organs, cerebral and aortic aneurysms, cardiac valvular abnormalities and renal failure. The genes responsible for the two most common forms of the disease have been identified. The PKD1 genes responsible for the most common forms of the disease have been identified. The PKD1 gene product is a probably membrane glycoprotein thought to mediate cell-cell or cell- matrix interactions. PKD2 is predicted to have 6 transmembrane domains and has modest homology to several types of ion channels. The cellular role of either protein has not yet been elucidated. This proposal brings together the collective expert5ise of investigators from multiple disciplines to tackle the problem in a "Center without walls". One project is a competitive renewal that aims to identify and characterize binding partners of human PKD1. The PI has shown that the C-terminus of PKD1 can bind to PKD2 and to an unusual Db1 family member of using multiple in vitro and in vivo methods. This proposal seeks to determine the biological relevance of the pr3eviously observed interactions. It also will continue the search for PKD1 binding partners in relevance of the previously observed interactions. It also will continue the search for PKD1 binding partners in fetal murine tissues obtained at a stage when PKD1 protein is known to be essential. Another project will characterize the functions of PKD2 in vivo and in vitro using a model experimental organism, Drosophila melanogaster. The proposed research takes a multi-disciplinary approach to the characterization of the Drosophila homologue of PKD2 using a combination of genetic, electrophysiological, cell biological, biochemical and molecular approaches. In the next project, the power of C. elegans molecular genetics to identify and define pathways of gene action will be applied to PKD function. The PI has found that the C. elegans homologue of PKD1 (LOV1) is essential for normal mating behavior and that the C. elegans homologue of PKD2 co- localizes to the same cell types. He will use this behavioral phenotype to determine the genetic pathways in which these gene products types. He will use this behavioral phenotype to determine the genetic pathways in which these gene products participate. The last project will determine the 3D structures of functionally important domains of PKD1 and PKD2 expressed in their native, non-disease state alone and in complex with each other. The PI of the Pilot and Feasibility has previously found that approximately 25% of vertebrate PKD1 has high homology to the Receptor for Egg Jelly of sea urchin sperm. In the current proposal, he will identify and characterize the sea urchin PKD2.